openntpd-openbsd/src/lib/libutil/fmt_scaled.3

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.Dd $Mdocdate: July 16 2016 $
.Dt FMT_SCALED 3
.Os
.Sh NAME
.Nm fmt_scaled ,
.Nm scan_scaled
.Nd handle numbers with a human-readable scale
.Sh SYNOPSIS
.In util.h
.Ft int
.Fn scan_scaled "char *number_w_scale" "long long *result"
.Ft int
.Fn fmt_scaled "long long number" "char *result"
.Sh DESCRIPTION
The
.Fn scan_scaled
function scans the given number and looks for a terminal scale multiplier
of B, K, M, G, T, P or E
.Pq in either upper or lower case
for Byte, Kilobyte, Megabyte, Gigabyte, Terabyte, Petabyte, Exabyte
.Po computed using powers of two, i.e., Megabyte = 1024*1024
.Pc .
The number can have a decimal point, as in 1.5K, which returns 1536
.Pq 1024+512 .
If no scale factor is found, B is assumed.
.Pp
The
.Fn fmt_scaled
function formats a number for display using the same
"human-readable" format, that is, a number with one of the above scale factors.
Numbers will be printed with a maximum of four digits (preceded by
a minus sign if the value is negative); values such
as 0B, 100B, 1023B, 1K, 1.5K, 5.5M, and so on, will be generated.
The
.Qq result
buffer must be allocated with at least
.Dv FMT_SCALED_STRSIZE
bytes.
The result will be left-justified in the given space, and NUL-terminated.
.Sh RETURN VALUES
The
.Fn scan_scaled
and
.Fn fmt_scaled
functions
return 0 on success.
In case of error, they return \-1, leave
.Va *result
as is, and set
.Va errno
to one of the following values:
.Dv ERANGE
if the input string represents a number that is too large to represent.
.Dv EINVAL
if an unknown character was used as scale factor, or
if the input to
.Fn scan_scaled
was malformed, e.g., too many '.' characters.
.Sh EXAMPLES
.Bd -literal -offset indent
char *cinput = "1.5K";
long long result;
if (scan_scaled(cinput, &result) == 0)
	printf("%s -> %lld\en", cinput, result);
else
	fprintf(stderr, "%s - invalid\en", cinput);

char buf[FMT_SCALED_STRSIZE];
long long ninput = 10483892;
if (fmt_scaled(ninput, buf) == 0)
	printf("%lld -> %s\en", ninput, buf);
else
	fprintf(stderr, "fmt scaled failed (errno %d)", errno);
.Ed
.Sh SEE ALSO
.Xr printf 3 ,
.Xr scanf 3
.Sh HISTORY
The functions
.Fn fmt_scaled
and
.Fn scan_scaled
first appeared in
.Ox 3.4 .
.Sh AUTHORS
.An -nosplit
.An Ken Stailey
wrote the first version of the code that became
.Fn fmt_scaled ,
originally inside
.Ox
.Xr df 1 .
.An Ian Darwin
excerpted this and made it into a library routine
(with significant help from
.An Paul Janzen ) ,
and wrote
.Fn scan_scaled .
.Sh BUGS
Some of the scale factors have misleading meanings in lower case
(p for P is incorrect; p should be pico- and P for Peta-).
However, we bend the SI rules in favor of common sense here.
A person creating a disk partition of "100m" is unlikely to require
100 millibytes (i.e., 0.1 byte) of storage in the partition;
100 megabytes is the only reasonable interpretation.
.Pp
Cannot represent the larger scale factors on all architectures.
.Pp
Ignores the current locale.